Water repellent coating compositions or sealers are generally low viscosity, colorless, penetrating liquids. One of the primary functions of these water repellent coating compositions is to prevent the penetration of liquid water into the pores of the substance to which the composition is applied. These water repellent penetrating compositions are designed to waterproof a variety of dry, porous substrates such as wood, brick, and concrete.
Water repellent coating compositions typically contain a nonvolatile composition. This nonvolatile composition contains the active water repellent ingredients. These ingredients remain on and penetrate into the treated substrate after the coating composition is applied and the liquid carrier evaporates. The active water repellent ingredients contained in the nonvolatile composition can include a variety of materials. These materials include various waxes, resins, acrylics, fragrances, preservatives and surface tension modifying chemicals.
The carrier used in a typical water repellent coating composition is usually a volatile organic compound ("VOC") so that the entire composition is organic. Recent actions by the Federal government to strengthen the air quality laws at the national level indicate that in the near future, all states will be required to mandate that only low VOC products be offered for sale nationwide. This reality has served to drive the research towards development of water-based equivalents to typical water repellent compositions that are consumer-acceptable. Research in the development of a consumer acceptable water-based water repellent coating composition has been ongoing for quite some time.
Unfortunately, the conventional surfactants that are used in these compositions are not typically volatile compounds and thus, when coated, remain after the water carrier evaporates. The hydrophilic portion of these compounds remain in the resulting coating and thus, greatly reduce the water repellency.
One potential alternative to the use of conventional surfactants are the recently developed hydrophobically modified high molecular weight polyacrylic acid copolymers. These compounds are typically used as thickening agents, primarily in cosmetic compositions. However, they also can serve as primary emulsifiers in oil-in-water emulsions and can emulsify compositions such as linseed oil, epoxy resins and asphalt. (Reference is made to BFGoodrich product bulletin "IS-9", CREATING EMULSIONS WITH CARBOPOL 1600-SERIES POLYMERS; and U.S. Pat. Nos. 4,923,940 and 4,966,274, assigned to BFGoodrich)
However, being primarily thickening agents, it is not surprising that these polymers produce coating compositions with conventional water repellent nonvolatiles that are quite viscous and thus, very difficult to apply in a manner similar to the VOC based water repellent compositions. In addition, the high viscosity inhibits the penetration of these compositions into porous substrates and this is undesirable.
Thus, there remains the need for water based water repellent coating compositions that can be easily applied and that can easily penetrate porous substrates. At the same time, the coatings that result from these compositions should provide excellent water repellancy, unlike compositions of this type that use conventional surfactants.